The traffic signal system community is lacking two major tools necessary for planning and operating state of the art traffic signal systems. First, there needs to be a rational procedure for quantifying the benefits associated with various traffic signal system improvements. Often, during the planning stage of a signal system upgrade many of the anticipated benefits are based upon percentage reductions in travel time, emissions, or delays observed in other systems. However, rarely are the systems so similar that these percentage reductions in measures of effectiveness (MOEs) are transferable. Furthermore, if a rational engineering economy-based decision model is followed, system costs and anticipated benefits should be tabulated to compute the net present value of benefits minus costs for a variety of alternatives such as 1) status quo, 2) coordinated fixed time system, 3) coordinated actuated-control system, 4) proprietary closed loop system, and, perhaps, 5) a new adaptive control model. Life cycle system costs are relatively simple to estimate. However, estimating the operational benefits can be quite difficult. Software packages such as CORSIM permit engineers to deterministically quantify benefits associated with cases 1, 2, and 3 for a particular study area. However, due to the large number of traffic signal system vendors, it is impossible to imagine CORSIM software developers ever implementing all the features necessary to model all the possible systems associated with cases 4 and 5. Therefore, there is a need for a systematic procedure to evaluate the benefits of control algorithms that are not available in the CORSIM environment.
Second, there needs to be a mechanism for tuning a new signal system off-line before it is deployed in the field. Modern traffic signal controllers have hundreds of different parameters that can be adjusted to improve system performance for a particular deployment. However, since traffic demand is stochastic and varies from day to day, there is no way to deterministically evaluate the performance gains or losses associated with parameter changes. Further, the political impact of making a mistake during an on-line tuning process leads to the fact that most modern closed-loop systems are deployed with many of their sophisticated traffic-responsive features non-operational. This is because traffic engineers cannot be certain of the performance of many of the newer adaptive features of closed loop systems and are unwilling to take the risk of attempting to make them functional.
Based on these observations, it is clear that a systematic evaluation procedure must be developed for evaluating and tuning traffic signal controllers before they are deployed on the street. It is currently possible to set up a complete closed loop system in a laboratory or signal shop environment with switch boxes (commonly referred to as a suitcase controller) connected to each controller. This type of test environment allows engineers to verify that desired controller features are operating as expected. However, to actually simulate all the discrete detector actuations that would be associated with a small three intersection arterial highway would be impossible for even small traffic volumes, much less with corridors with more signals or higher traffic volumes. Furthermore, it would be impossible to quantify the performance of such a simulation in terms of vehicle travel time or delay. Alternatively, if a testing environment could be set up where a computer operated the switch boxes and kept track of vehicle movements throughout a system, quantitative performance measurements could be obtained.